Six buses carrying children were escorted by security forces in Niger State on Monday, according to an AFP reporter on site in the regional capital, Minna.
Nigeria's government says the children, as well as seven teachers, were the last to be held captive by the kidnappers who attacked the St Mary's Catholic School.
The children appeared to be between the ages of four and ten, according to AFP.
There is no information about the circumstances surrounding the release.
Mass kidnappings are a recurring occurrence in Nigeria, and for criminal and armed groups, it can be a way to obtain significant ransoms.
